1. Field of the Invention
The present invention relates to a sealing device intended more especially for providing the upstream/downstream sealing of a valve.
It applies more particularly to valves of the type comprising a valving member movable inside a tubular body and comprising, at its periphery, a sealing surface coming to bear, at the end of the valving stroke, on a circular sealing packing, after a movement tangent or parallel to the main axis of symmetry of said sealing packing.
The invention is also suitable for valves in which, in a reverse installation, the bore of the body comprises a substantially conical sealing surface and the valving member has at its periphery a packing providing static sealing with the valving member and dynamic sealing with said sealing surface.
Thus, in these types of valves, the sealing packing must fulfil multiple functions. It must at one and the same time provide static sealing, dynamic sealing and continuity of sealing between the static seal and the dynamic seal.
These sealing functions are particularly delicate to provide, more particularly in the case where, because of the operating conditions of the valve, the sealing packing must be made at one and the same time from a soft material capable of adapting itself to the surface state of the bearing surface of the seat so as to provide the best sealing, from a hard and rigid material capable of withstanding the mechanical forces due to the packing/seat contact pressure and to the pressure of the fluid to be sealed and sufficiently flexible for allowing relative sealing member/body movements without adversely affecting the sealing.
In fact, in the case where, in the closed position of the valve, the sealing surface of the valving member is not exactly centered on the dynamic liquid tight bearing surface of the packing, this latter is not uniformly compressed, so that an homogeneous seal is not obtained all around the valve. Thus, in the portions where the packing is highly compressed by the valving member, the valve may thus stand high pressures whereas, in the portions diametrically opposite these latter, the seal is doubtful and the risks of high pressure leaks are high.
2. Description of the Prior Art
To overcome these drawbacks, the valves have been fitted with mechanisms for centering the valving member with respect to the sealing packing, these mechanisms concerning either the kinematics of the valve or the valve itself.
However, these solutions are complex, unreliable and cause a considerable increase in the cost price of the valves.
It has also been proposed to provide the sealing packing in the form of a double flexible metal O-seal comprising:
a first flexible metal O-seal structure providing static sealing with the body of the valve,
a second flexible metal O-seal structure providing the dynamic sealing,
a radial membrane made from a resilient material connecting the two sealing structures together while enveloping them at least partially so as to provide continuity of sealing between the static seal and the dynamic seal, and to allow both self centering of the second seal structure on the sealing surface of the valving member, and
a floating reaction ring, applied against the second seal structure opposite the zone of this structure where the sealing surface of the valving member comes to bear.
Such a sealing packing which is described in French Pat. No. 77 22976 of the 26th July 1977 in the name of the applicant for: "Double Flexible O-seal", allows excellent results to be obtained more especially in the case of valves or cocks intended to operate under conditions (high or low temperatures) for which the use of conventional elastomer packings is prohibited.
The object of the invention is more particularly to extend the self centering concept characteristic of the double flexible metal O-seal previously described to metal sealing structures having simplified structures, which may be more easily constructed and designed so as to simplify and considerably reduce the cost of fitting them in the body of the valve, not only in so far as the cost of the parts used is concerned and the machining operations required on the body but also the cost of the fitting operation properly speaking.
It should be noted that the invention is not limited solely to a simple sealing packing but to the whole of the arrangements used in combination with the structure and conformation of this sealing packing so as to obtain the desired results.